Engines are required to operate under increasingly demanding conditions. The loads applied to the engine, and the harshness of the surrounding environment, place a great amount of stress on an engine. Therefore, consistent monitoring of the condition of the oil is increasingly important.
Currently, the condition of engine oil, i.e., when the useful life of the oil has ended, is estimated by monitoring the length of time the oil is in use, and modifying the estimate by accounting for the conditions under which the engine operates. The estimate is used to determine the interval, in time or mileage, between oil changes. However, the condition of the oil at any given time cannot be determined by this method.
In addition, the estimate may not accurately determine the useful life of the oil. Therefore, the oil may be changed too frequently, which adds unnecessary maintenance costs, or not frequently enough, which causes undue wear on the engine.
Attempts have been made to monitor the condition of engine oil in real time by monitoring one or more parameters of the oil that lead to oil deterioration. For example, during combustion of fuel in an engine, some of the fuel only partially combusts. The by-product of this partial combustion is known as soot. Soot is deposited during each combustion cycle on the walls of each cylinder in an engine due to the relatively lower temperatures on the walls; thereby preventing full combustion from occurring. The rings on the pistons then wipe this soot off the cylinder walls and deposits the soot into the oil that lies in the crankcase of the engine.
The accumulation of soot in the oil is a direct indicator of oil condition. Therefore, research has resulted in methods and systems to monitor the amount of soot in oil, which can be used to determine the condition of the oil.
For example, in U.S. Pat. No. 5,548,393, Nozawa et al disclose an apparatus for detecting the amount of soot in oil. The apparatus includes a light-emitting device that emits a light which is reflected by a chamber containing the oil. The amount of light reflected is used to indicate the amount of soot in the oil. As the concentration of soot increases, the amount of reflected light decreases.
However, the relationship of reflected light to soot concentration is not linear. For small amounts of soot, the change in reflected light to a change in soot concentration can be easily measured. As the amount of soot increases, the rate of change in the light that is reflected diminishes. Therefore, the change in reflected light for a change in heavily concentrated soot becomes much more difficult to measure. As a result, determining the amount of soot in oil as the oil nears the end of its useful life cannot be done accurately.
Other techniques for measuring the amount of soot in oil are not practical for use in real time. In one example, a method to measure soot results in heating a sample of oil under controlled conditions until the oil evaporates. The remaining residue, soot, can then be measured. This method would not be practical to determine the amount of soot while the engine is operating.
The present invention is directed to overcoming one or more of the problems as set forth above.